When I got the Mustang it had drum brakes all around. Stopping was not easy. During my restoration I added in disc brakes for the front. The kit was a refinished parts from a Ford Granada. They fit fine and the only draw back was that I had to get larger wheels to clear the brake caliper. Then I found a Power Booster for the brakes. That should definitely improve the stopping power! Well here are some pics.
The clearance from the firewall to the shock tower didn't allow room for a cast iron type of fluid reservoir. Well I could make it fit but the support running from the shock tower to the firewall would cover the top and not allow you to open the top to add fluid so they shipped it with this plastic one.
My decision to add this non-stock setup with disc brakes and booster is about the only thing that bothers me about trying to keep it factory. But I really wanted improved stopping power.